Overload Effects on Fatigue Fracture Surfaces
Final technical rept.
SRI INTERNATIONAL MENLO PARK CA
Pagination or Media Count:
The effects of overloads on fatigue fracture surfaces of titanium and nickel alloys were investigated with advanced fractographic techniques. Fracture surface topographies were mapped quantitatively by confocal microscopy and analyzed by comparing conjugate topographs the FRASTA technique to measure the deformation at locations of overload. Insight into plastic zone development was obtained from computational simulations of fatigue tests with the LSDYNA3D code. FRASTA detected the remnants of plastic blunting on Ti alloy fracture surfaces even though the deformation was not perceptible with an SEM and indicated the bluntness as the amount of deviation from a FRASTA-generated fracture progression curve. Under certain conditions of stress ratio, the deviation related to the magnitude of the overload. Results for other stress ratios and IN 100 nickel alloy tested at 650 degrees centigrade were less clear. Nevertheless, a procedure for detecting the occurrence of overloads from failed parts has been demonstrated. Moreover, if these initial findings can be confirmed, expanded, and related to cyclic load spectra, then fatigue retardation models, and hence, lifetime prediction capability can be improved.
- Fabrication Metallurgy